Hydraulic reciprocating device



July 21, 1964 H. N. HOFFMAN 3,141,384

HYDRAULIC RECIPROCATING DEVICE Filed Dec. 5, 1962 INVENTOR'. 20 HERBERT N. HOFFMAN,

W.Z.M

HIS ATTORNEY.

United States Patent 3,141,384 HYDRAULIC RECKPROCATING DEWCE Herbert N. Hofiman, Luuenburg, Mass, assignor to General Electric Company, a corporation of New York Filed Dec. 3, 1962, Ser. No. 241,657 3 Claims. (Cl. 91-53) This invention relates to an improved hydraulic reciprocating device suitable for powering a pawl-and-ratchet mechanism to operate a turbine rotor turning gear.

Hydraulically powered reciprocating devices find many applications, one of these being to actuate a spring loaded pawl which engages ratchet teeth on a turbine rotor. This serves to slowly turn the rotor when the turbine is shut down to prevent bowing of the rotor from unequal temperature distribution. 'of reciprocating devices employs a double-acting hydraulic cylinder which actuates electrically-actuated or cam-oper- One of the more common types ated pilot valves at either end of its stroke to reverse the flow of hydraulic fluid to the main piston. Such devices are subject to failure from accumulation of dirt in the pilot valves, which are relatively easy to jam. Sensitivity to binding from dirt in the hydraulic fluid is characterisitc of many prior art reciprocating devices.

Accordingly, one object of the present invention is to provide an improved hydraulic reciprocating device which is reliable and relatively insensitive to sticking or jamming due to foreign particles in the hydraulic liquid.

Another object of the invention is to provide an improved hydraulic reciprocating device having a single-acting power piston, together with provision for automatically engaging a pawl and ratchet mechanism which is operated by the piston.

The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the concluding portion of the specification. The invention, however, both as to organization and method of practice, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawing, in which the single figure is an elevation view, partly in section, showing the preferred embodiment of the invention.

Briefly stated, the invention is practiced by providing a single-acting main piston having a bypass valve therein which is actuated by a separate valve piston attached to the bypass valve stem. The valve piston opens and closes ports to control the flow of liquid to the main piston, while the opening and closing of the bypass valve effects the reciprocating movement of the main piston. The bypass valve is activated by relative movement between the main piston and the valve piston, caused, in turn, by restriction of the flow of fluid to the valve piston. An auxiliary piston automatically swings the pawl into engaging position with the cooperating ratchet wheel on each stroke.

Referring to the single figure of the drawing, a cylindrical housing 1 defines a main cylinder 2 and a connecting smaller diameter secondary cylinder 3. Housing 1 is open at either end, and is provided with a bottom closure piece 4 and a top 5, both attached by bolts as shown.

Disposed in the main cylinder 2 is a main piston 6, with a suitable abutment 6a, to prevent the piston from bottoming in the cylinder. A main piston stem 7 extends upwardly through a central bore a in top 5, and is sealed against leakage by a suitable packing 8. Main piston stem 7 is welded at its lower end to a cup-shaped member 9 which, in turn, is bolted to main piston 6. A main compression spring 10 is held between suitable receiving surfaces on top 5 and cup-shaped member 9.

A pawl bracket 11 is fixed to the upper end of main 3,141,384 Patented July 21, 1964 "ice piston stem 7 to provide a pivoted support on pin 12d for pawl 12. Pawl 12 has a ratchet-engaging portion 12a, a spring loaded arm 12b, and an actuating arm 120. The pawl engages a ratchet wheel 38 attached to the turbine rotor (not shown). Pawl bracket 11 also houses a slidable pin 13, which is forced against pawl arm 12b by a spring 14, thereby biasing the pawl 12 clockwise about pivot 12d to the position shown. This clockwise rotation is limited by engagement of transverse stop pin 12e with the adjacent side of bracket 11.

Hydraulic fluid may be bypassed from the lower side of piston 6 to the upper side thereof by means of a bypass valve disc 15 disposed to cooperate with a valve port 612 in the center of piston 6. Port 6b communicates freely with the upper side of piston 6 by means of open ings 16 and 17 in the cup-shaped member 9. Bypass valve 15 is biased toward closed position by a compression spring 18 situated between the top of valve 15 and the top of cup-shaped member 9. Spring 18 must be of suificient size so that oil pressure under main piston 6 alone will not cause bypass valve 15 to open.

The stem 19 of bypass valve 15 extends downwardly into secondary cylinder 3, where it is loosely attached to a valve piston 21 The valve piston 20 is held loosely between a flange 19a and a washer 21 on the end of stem 19. A nut 22 is adjusted to provide a small axial clearance 19b. A cover plate 20a prevents leakage of fluid along stem 19. The top of piston 20 is also spaced from abutment 6a by a clearance 20b which is larger than clearance 1917, so that when piston 20 is against flange 19a, the piston and flange can both move upward relative to piston 6.

The upper end of valve piston 20 has a number of circumferentially spaced longitudinal grooves 23, and also has a circumferential groove 24, which creates a precision cutoff land 25, on piston 20. Cooperating when land 25, with piston 20 is near the top of its stroke, is a circumferential oil supply groove 26 in the wall of cylinder 3. Thus fluid can flow from supply groove 26 through the longitudinal grooves 23 to the bottom of main piston 6, until flow is cut off by land 25 of valve piston 20 covering the supply groove 26.

There is also a second oil supply passage 27, in housing 1, which furnishes a restricted flow of oil through a plug orifice 28 to the pressure chamber 3a at the lower end of valve piston 20. Circumferential supply groove 26 and pasage 27 are both supplied by an inlet passage 29. The passage 29 is connected to a source of hydraulic fluid under pressure (not shown) by means of a connecting pipe 30 having a flow restricting orifice 31.

Pawl 12 is automatically moved into engaging position with ratchet 38 by means of an auxiliary single-acting pawl piston 32 contained in an auxiliary cylinder 33 mounted on top of housing 1. Pawl piston 32 is biased to its downward position by means of a compression spring 34, and includes a projecting stem 35 arranged to actuate arm of pawl 12. Hydraulic fluid is supplied to the lower side of pawl piston 32 by means of a pipe 36, which also receives oil from conduit 30 at the downstream side of orifice 31.

The reciprocating device is shown with the main piston 6, valve piston 20, bypass valve 15, pawl piston 32, and pivotable pawl 12, in retracted position. The extended positions of these members are indicated in phantom lines in order to facilitate description of the operation. The members are designated in the extended position by the same numerals, but with a prime superscript, i.e., main piston 6, valve piston 20', bypass valve 15', pawl piston 32, and pawl 12'.

It remains to note that, as shown by the extended" positions of the members, the pawl piston 32' has a relatively short stroke so as to leave a substantial clearance space 37, between the extended stem 35 of the pawl piston and arm 120 of the pawl in their uppermost positions. The pawl 12 is of course held thus by engagement with the ratchet gear 38 during the upward stroke of the piston 6. Also, valve piston 20 is designed to have a greater stroke than main piston 6, so that when piston 6 is at the top of its stroke (position 6'), valve piston 20 can continue to move, against the bias of bypass valve spring 18, thereby lifting bypass valve 15 from its seat as shown in the phantom lines 15, 6b.

The operation of the improved hydraulic reciprocating device will be apparent from the following description. A restricted flow of hydraulic fluid under pressure is supplied through orifice 31 to conduits 30, 35. The hydraulic fluid from 36 enters the lower end of auxiliary cylinder 33 and forces pawl piston 32 upward against spring 34 to pivot pawl 12 counterclockwise about pivot 12d, so that portion 12a thereof can engage the teeth of ratchet wheel 38. The pawl piston 32 and spring 34 are sized and selected, by means known to those skilled in the art, so that the pawl will be actuated before main piston 6 starts to move.

Simultaneously, hydraulic fluid enters passage 25 and flows from circumferential groove 26 to the lower side of main piston 6, forcing it upward at a rate determined by the rate of flow through supply orifice 31. Oil also flows through passage 27, and through orifice 28, to the lower end of valve piston 25.

The rate of flow through orifice 28, however, is further restricted so that the pressure will build up faster under main piston 6 than it will under valve piston 20. Therefore, main piston 6 moves upward, pulling valve piston 25 upward with it. This restraining force by valve piston 2t) maintains the clearance 1% under flange 19a, and also keeps bypass valve disc 15 seated on valve seat 6b.

This upward movement continues until land 25 of valve piston 20 blocks groove 26, thus shutting off flow to piston 6, which stops moving. Liquid continues to flow through orifice 23, first moving piston 20 along stem 19 to close the clearance gap 1% and provide overtravel past groove 26, which prevents governing. Then continued flow through orifice 28 causes piston 20 to exert an upward force on bypass valve stem flange 1%. Pressure continues to build up under piston 20 until the force exceeds the closing bias imposed on bypass valve 15 by the spring 18, whereupon valve piston 2t moves upward, relative to the main piston 6, to the extent permitted by clearance 20b, opening bypass valve 15. When this occurs, the fluid pressure is released below piston 6 as the oil flows through bypass valve 15 and escapes from cylinder 2 through drain port 1a.

Piston is now free to move downward under the bias of spring 10. However, the liquid below valve piston 20 must escape at a restricted rate through plug orifice 28, and the rate of descent is controlled by the rate of flow permitted backwardly through orifice 28, to drain port 1a. Meanwhile, the pressure below valve piston 25 maintains bypass valve 15 in its open position against spring 18 as main piston 6 descends.

It will be noted that pawl piston 32, at the start of retraction, is still in an extended position, since the pressure in passage 29 is maintained by land 25 blocking groove 25. However, the clearance space 37 allows the main piston 6 and valve piston 20 to descend so that groove 26 is unblocked, whereupon the liquid below pawl piston 32 can also escape through bypass valve 15 faster than it is supplied through orifice 31, to allow the pawl piston 32 to be retracted by spring 34.

When main piston 6 reaches. the bottom of its stroke, the bypass valve 15 is still open by virtue of the pressure remaining below valve piston 20. This pressure is chamber 3a will continue to drop as oil flows backward through orifice 28, until spring 18 closes bypass valve 15. Thereupon the cycle commences again.

It will be observed that the construction does not employ any small-diameter pilot valves which might be relatively sensitive to jamming or sticking from dirt particles. The supply of fluid to main piston 6 is effected by the valve piston 2b, which has a relatively large cut-ofi land 25, and the force which causes it to move is created by the main piston 6. The bypass valve 15 is likewise of relatively large capacity and substantially insensitive to sticking.

Another feature of the invention is that the pawl 12 is pivoted to the engaged position 12 only on the upward stroke. On the downward stroke, it is disengaged by the spring-loaded pin 13, so that it will not cause wear on the teeth of ratchet wheel 38.

This hydraulic reciprocating device is, of course, not limited to use with a pawl engaging mechanism as shown, since many other applications are possible. However, the particular arrangement shown provides the feature of automatically engaging and disengaging the pawl mechanism so as to provide a highly reliable and trouble-free turning gear for a turbine rotor.

While there has been described herein What is at present considered to be the preferred embodiment of the invention, it will be understood that various modifications may be made, and it is intended to cover in the appended claims all such modifications as fall within the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A hydraulic reciprocating device comprising:

a housing defining primary and secondary cylinders,

main piston means disposed in the primary cylinder and having a bypass valve disposed therein to pass fluid from one side of the main piston means to the other,

first means biasing the main piston means to a retracted position,

second means biasing the bypass valve to a closed position, the force of the second biasing means on the bypass valve being in the same direction as the force of the first biasing means on the main piston means,

valve piston means disposed in said secondary cylinder and connected to actuate the bypass valve and to cut off the flow of fluid to the main piston means when both the main and valve piston means are in an extended position,

a source of hydraulic pressure fluid, and

conduit means supplying a first restricted flow of fluid from said source to actuate the main piston means against the first biasing means, said conduit means also supplying a second, more restricted flow of fluid to actuate the valve piston means against the second biasing means, whereby the valve piston means will move relative to the main piston means against the second biasing means when the fluid supply to the main piston means is cut off, thereby opening the bypass valve and causing the main piston means to retract under the influence of the first biasing means.

2. A hydraulic reciprocating device comprising:

a housing defining coaxial primary and secondary cylinders,

a main piston disposed in the primary cylinder,

a bypass valve disposed in the main piston and constructed to pass fluid from one side of the main piston to the other when the bypass valve is open, the bypass valve also having a stem extending into the secondary cylinder,

first means biasing the main piston toward the secondary cylinder to a retracted position,

second biasing means disposed on the main piston and biasing the bypass valve toward a closed position in the direction toward the secondary cylinder,

a valve piston disposed in the secondary cylinder and disposed to actuate the stern of the bypass valve.

first conduit means providing access of fluid to both primary and secondary cylinders when the main and valve pistons are in retracted position and arranged to be interrupted by the valve piston when said pistons are in an extended position,

second conduit means providing a restricted flow passage to the side of the valve piston remote from the bypass valve, and

a source of pressure fluid supplying a limited flow of hydraulic liquid to said first and second conduit means,

3. A hydraulic reciprocating device for effecting stepwise rotation of a ratchet wheel comprising:

a housing defining coaxial primary and secondary cylinders,

a main piston disposed in the primary cylinder with a piston rod projecting from the end of the cylinder,

a pawl member pivotably carried on said piston rod and disposed to move into engaging relation with a ratchet wheel,

hydraulically actuated means on said housing and connected to move said pawl into ratchet engaging relation,

a bypass valve disposed in the main piston to pass fluid from one side of the main piston to the other, the bypass valve having a stern extending toward the secondary cylinder,

first spring means biasing the main piston to a retracted position in a direction toward the secondary cylinder,

second spring means disposed on the main piston and biasing the bypass valve toward a closed position which is also in the direction of the secondary cylinder,

a valve piston disposed in the secondary cylinder and connected to actuate said bypass valve stem,

first conduit means arranged to communicate between the primary and secondary cylinders when the pistons are in a retracted position, said valve piston having a portion disposed to block off the first conduit means from communication with the primary cylinder when the pistons are in extended position,

orifice means providing a restricted passage for admitting pressure fluid to the secondary cylinder on the side of the valve piston away from the bypass valve,

and a source of hydraulic pressure fluid providing limited flow to the pawl actuating mechanism and to the first conduit means, whereby the pawl is moved to ratchet engaging position at the start of the working stroke of the main piston and the valve piston actuates the bypass valve to release the pressure on the main piston and on the pawl actuating means to retract the pawl from ratchet engaging relation during the return stroke of the main piston.

References Cited in the file of this patent UNITED STATES PATENTS 2,477,359 Barksdale July 26, 1949 2,572,162 Koonz Oct. 23, 1951 2,603,191 Sterrett July 15, 1952 2,630,181 Solum Mar. 3, 1953 2,649,078 Kelly Aug. 18, 1953 2,802,452 Hogeman Aug. 13, 1957 3,082,596 McGay et a1. Mar. 26, 1963 FOREIGN PATENTS 62,432 Switzerland Oct. 30, 1912 

1. A HYDRAULIC RECIPROCATING DEVICE COMPRISING: A HOUSING DEFINING PRIMARY AND SECONDARY CYLINDERS, MAIN PISTON MEANS DISPOSED IN THE PRIMARY CYLINDER AND HAVING A BYPASS VALVE DISPOSED THEREIN TO PASS FLUID FROM ONE SIDE OF THE MAIN PISTON MEANS TO THE OTHER, FIRST MEANS BIASING THE MAIN PISTON MEANS TO A RETRACTED POSITION, SECOND MEANS BIASING THE BYPASS VALVE TO A CLOSED POSITION, THE FORCE OF THE SECOND BIASING MEANS ON THE BYPASS VALVE BEING IN THE SAME DIRECTION AS THE FORCE OF THE FIRST BIASING MEANS ON THE MAIN PISTON MEANS, VALVE PISTON MEANS DISPOSED IN SAID SECONDARY CYLINDER AND CONNECTED TO ACTUATE THE BYPASS VALVE AND TO CUT OFF THE FLOW OF FLUID TO THE MAIN PISTON MEANS WHEN BOTH THE MAIN AND VALVE PISTON MEANS ARE IN AN EXTENDED POSITION, A SOURCE OF HYDRAULIC PRESSURE FLUID, AND CONDUIT MEANS SUPPLYING A FIRST RESTRICTED FLOW OF FLUID FROM SAID SOURCE TO ACTUATE THE MAIN PISTON MEANS AGAINST THE FIRST BIASING MEANS, SAID CONDUIT MEANS ALSO SUPPLYING A SECOND, MORE RESTRICTED FLOW OF FLUID TO ACTUATE THE VALVE PISTON MEANS AGAINST THE SECOND BIASING MEANS, WHEREBY THE VALVE PISTON MEANS WILL MOVE RELATIVE TO THE MAIN PISTON MEANS AGAINST THE SECOND BIASING MEANS WHEN THE FLUID SUPPLY TO THE MAIN PISTON MEANS IS CUT OFF, THEREBY OPENING THE BYPASS VALVE AND CAUSING THE MAIN PISTON MEANS TO RETRACT UNDER THE INFLUENCE OF THE FIRST BIASING MEANS. 